1. Field of the Invention
The present invention generally relates to electrical cables, and more particularly to electrical cable strain reliefs and methods of manufacture thereof.
2. Background Information
Strain reliefs are used in generally all electrical components having power cords needing to be plugged into a wall receptacle. These power cords typically extend through an opening in the case or housing of the component. If left unprotected, the power cord would soon fray due to the friction of rubbing against the case opening.
A first purpose of a strain relief is to protect the electrical cord from rubbing against the edges of the opening. A second purpose of a strain relief is to relieve bending strains in the cord as it bends at or near its connection with the opening.
FIG. 1 and FIG. 2 show a common type of prior art strain relief. This type strain relief has a threaded first piece 2 which is typically fastened to the body of the appliance through use of a threaded nut (not shown). This first piece 2 has an extended compression ring through which the wire 5 is inserted. The threaded second piece 4 of the strain relief is then threaded on and compresses the compression ring against the wire. This works reasonably well except in heavy duty applications, such as in commercial vacuum cleaners.
The problem is that as the wire and the threaded strain relief are continuously pulled, twisted and flexed, the compression ring is working fixedly against the power cord, and eventually will start to fray and break the metal strands within the wires within the cord. When this occurs, it will eventually result in a dead short and the heat from the short will melt the threaded strain relief
A second type of prior art strain relief is used on some lighter duty appliances. These strain reliefs are a single piece which is directly molded on the cord. They are formed by placing the wire cord in a jig, closing up the jig, and injecting PVC to directly bond the strain relief to the outer jacket of the electric cord. However, this is not done with threaded ends because the material is not strong enough to hold a threaded end. This type of direct, injected strain relief is typically used on thin, plastic cases for appliances where the soft cord has a washer-like protrusion on the end which fits into notches between two halves of the case that are then later joined together.
What is needed is a strain relief which overcomes the shortcomings of the prior art. The present invention serves this purpose.
The present invention is a two-part strain relief. At one end is a threaded end which is hard, preferably glass-filled nylon, which is slid over the cord. The threaded end has two flanges attached to it, and has holes in its shaft so that when direct molded PVC (or other pliable material) is later injected, the PVC will go through the holes and encase the two flanges thereby holding the threaded end tightly bonded to the flexible PVC end.
With this new type of strain relief, there is no compression of the cord, and as a result its life expectancy is significantly greater. The hard threaded end is amenable for use in a variety of applications, from extending through a hole in a metal container, and more importantly, through a hole in a rotational molded container where the thickness of the roto-molded container case wall can vary substantially from part to part, thus necessitating the use of a threaded end.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.